Nanofluids droplets evaporation kinetics and wetting dynamics on rough heated substrates.

The influence of aluminium nanoparticles on the evaporation and wetting dynamics of ethanol sessile droplets on a heated PTFE surface is investigated experimentally. The experimental technique uses a goniometer to measure the evolution in time of the shape of the droplets (contact angle, base diameter and volume). The evaporation rate is deduced from the measurements of the evolution of volume in time. During the "pinning" phase and contrary to what is expected, the presence of nanoparticles leads to a reduction of the evaporation rate compared to the base fluid. It is found that the deposition of nanoparticles into the triple contact line wedge during the evaporation of the droplet causes a greater pinning time for nanofluid droplets. The overall evaporation time for base fluid droplets is found to be longer than for nanofluid ones. The wetting dynamics of the droplets throughout the evaporation process shows major influence of nanoparticles. Depinning contact angles tend to be larger for nanofluid droplets than for base liquid ones. Over a range of imposed substrate temperatures, no effect on the nanofluids depinning contact angle is observed. The alteration of contact line behavior as well as wettability can have important implications in a wide range of applications, e.g. two phase boiling heat transfer [Kim, S. J. et al., Appl. Phys. Lett., 2006, 89, 153107].